Scientists have found a new way of discovering if alien life exists on a planet.
Gases on a planet could be the vital sign of alien life
Researchers at the University of California, Riverside (UCR) have discovered that signatures of greenhouse gases - such as methane, ethane and propane - would be a major sign that a planet has been terraformed (artificially altered) by another form of life.
Scientists conducted simulations on a hypothetical planet and discovered that NASA's James Webb Space Telescope could spot the gases easily.
UCR astrobiologist and lead author of the study Edward Schwieteman said: "For us, these gases are bad because we don't want to increase warming.
"But they'd be good for a civilisation that perhaps wanted to forestall an impending ice age or terraform an otherwise uninhabitable planet in the system, as humans have proposed for Mars."